/Engine/Source/Runtime/Renderer/Public/InstanceCulling/InstanceCullingContext.h
Allocate indirect arg slots for all meshes to use instancing, add commands that populate the indirect calls and index & id buffers, and Collapse all commands that share the same state bucket ID NOTE: VisibleMeshDrawCommandsInOut can only become shorter.
void SetupDrawCommands ( [TArrayView](API\Runtime\Core\Containers\TArrayView)< const [FStateBucketAuxData](API\Runtime\Renderer\FStateBucketAuxData) > StateBucketsAuxData, FMeshCommandOneFrameArray & VisibleMeshDrawCommandsInOut, bool bCompactIdenticalCommands, int32 & MaxInstancesOut, int32 & VisibleMeshDrawCommandsNumOut, int32 & NewPassVisibleMeshDrawCommandsNumOut )